1. Field of the Invention
This invention generally relates to monolithic microwave integrated circuit devices and, in particular, to such devices which may be used as noise sources and as variable resistors.
2. Statement of the Prior Art
Noise sources are typically used in the fabrication and testing of microwave systems, such as receivers, for the purpose of determining the amounts of additional noise generated within such systems. Existing noise sources generally take the form of avalanche noise diodes carried in waveguide mounts which may be connected to different types of microwave circuitry (waveguide, stripline, MMIC) by the use of appropriate physical couplers. As useful as these known devices have been, they are still less suitable for more modern microwave systems which have tended towards higher frequencies and smaller component and circuit sizes. Existing devices are especially excluded from built-in-test (BIT) applications because of the physical differences in the circuit types.